Is there a circular baffle that we should be looking at also? Is the reason for the extended baffle to help with phase or extend ??????? JP

As always, feel free to get creative with supra-baffles and report findings - but the arrangement pictured was intended a much as anything to accommodate drivers that would otherwise be tricky to install -

We designed our "kit" to allow for easy build with a minimum of tools / clamps etc - the front panel/driver baffle is inset (dadoed) into the side; any driver requiring cutouts approaching the 140mm internal would reduce the integrity of this piece, hence the wider plant-on baffle - which also allows for swapping out drivers of different dimensions and rebated cut-outs.

I finally snuck some time to do a 1st version of the promised 4L FE126En centre for those using FE126En FH3 in HT systems.

This does not go really low (almost reaches 100 Hz), but is as good as you can get in a BR without the shape of the roll-off becoming a bad joke (a reference to a comment Cal made about the factory 10L BR).

To follow to make materials sourcing more universal: 15/18mm and 5/8 3/4" can be done. Also 9.5mm (3/8") vents.